1. Field of the Invention
The present invention relates to a ball screw device used in a feed mechanism, etc. of a moving body of a machine tool, a precision machine, etc., and particularly used in a feed mechanism of high speed, etc.
2. Description of the Related Art
The ball screw device is generally coated with a lubricant of grease, etc. and is smoothly operated by forming an oil film between a shaft rolling groove of a screw shaft, a nut rolling groove of a nut and a rolling ball. However, the function of grease, etc. as the lubricant is reduced in a comparatively short period by the influences of temperature, moisture, foreign matters, etc. Therefore, it is necessary to periodically make a replenishing work of the grease, etc.
In the related ball screw device, the shaft rolling groove of a spiral shape arranged in the screw shaft and the nut rolling groove opposed to the shaft rolling groove and arranged in the nut are screwed through the rolling ball so as to solve such complicatedness of the replenishing work. Further, a lubrication ring in an annular shape constructed by a lubricant-including polymer having a resin material comparatively rich in elasticity as a base material is arranged in an end portion of the nut. The inner surface of this lubrication ring comes in slide contact with the outer surface of the screw shaft and the screw shaft is lubricated. Further, the invasion of foreign matters such as dust, etc. is prevented by a seal body arranged outside the lubrication ring (e.g., see JP-A-2000-81103).
JP-A-2000-81103 (paragraph 0020 of page 3 to paragraph 0037 of page 5, and FIGS. 1 and 2) is referred to as a related art.
However, in the above related art, the seal body for preventing the invasion of the foreign matters is arranged so as to come in slide contact with the outer surface of the screw shaft. Therefore, the lubricant exuded from the lubrication ring including the lubricant is scraped by the seal body, and the lubricating state of a slide contact surface of the lubrication ring made of a material comparatively rich in elasticity becomes unstable. Therefore, there is a case in which a stick slip phenomenon is generated. In this stick slip phenomenon, deformation due to catching in a part insufficient in the lubricant and restoration due to the elasticity of the lubrication ring are discontinuously caused.
This phenomenon is not generated when the screw shaft is rotated at low speed. However, when the screw shaft is rotated at high speed and is suddenly accelerated and decelerated, this phenomenon is easily generated. When this phenomenon is generated, a self-excited vibration is caused by this phenomenon and an abnormal sound is generated.